国产高强度Q960钢高温蠕变及其对钢柱抗火性能影响

为获得国产高强度Q960钢高温下蠕变应变,对Q960钢进行高温拉伸蠕变试验,得到不同温度和应力水平下的蠕变应变-时间曲线,基于试验数据,提出适用于Q960钢结构抗火分析的蠕变模型。采用有限元模型分析蠕变效应对Q960钢柱抗火性能的影响,得到标准升温条件下无防火保护Q960钢柱的临界温度,并与《建筑钢结构防火技术规范》(GB-51249)计算的结果进行对比。研究表明：当温度超过600℃时,Q960钢材具有明显的蠕变效应,且温度越高,断裂前蠕变总变形越大;蠕变效应会显著降低Q960钢柱的临界温度和耐火极限;《建筑钢结构防火技术规范》(GB-51249)中的临界温度法不适用于Q960钢柱,当荷载比小于0.75时,计算结果不安全,而荷载比大于0.75时,计算结果偏于保守。     

盾构隧道环间纵向压力时变规律研究

盾构隧道断面上受到纵向压力的大小,一方面影响环缝止水垫的防水性能;另一方面影响环缝刚度,从而影响隧道纵向不均匀沉降的发展。目前实际工程中主要依据经验估测隧道中残留的纵向力。通过求解描述隧道受力变形特征的微分方程,建立了隧道任意断面纵向力随时间的变化关系,并将理论解与现场试验实测结果进行了对比,二者具有良好的匹配性。研究结果表明,隧道纵向力在波动中下降,最终残留的纵向力大小与混凝土徐变系数和周围土体的压缩模量有关,约为掘进阶段千斤顶顶力的20.4%~44%。     

Tensile,creep and fatigue behaviours of short fibre reinforced polymer composites at elevated temperatures: a literature survey

Polymer composites are suitable alternatives to metals in some applications as they are cost effective, lightweight and corrosion resistant. Short fibre reinforced polymer composites (SFRPCs) are typically subjected to complex loadings in applications, including static, cyclic, thermal and their combinations. These applications may also involve harsh environmental conditions such as elevated temperature and moisture which can dramatically affect mechanical properties. In this paper, a broad survey of the literature on mechanical behaviour of SFRPCs at elevated temperatures is presented. The mechanical behaviours included consist of tensile, creep, isothermal fatigue, thermo‐mechanical fatigue and creep–fatigue interaction. Environmental effects such as moisture and ageing at elevated temperatures are also included. The studies reviewed include experimental works, modelling works and failure mechanisms studies. A critical assessment of the information from the literature presented for each type of behaviour is also provided.     

A quantitative metallographic assessment of the evolution of porosity during processing and creep in single crystal Ni‐base super alloys

The present work reviews previous research on the evolution of porosity. It presents new results from a detailed study on the evolution of porosity during casting, heat treatment and creep of a single crystal Ni‐base superalloy subjected to uniaxial tensile creep at 1050 °C and 160 MPa in [001] and [110] directions. A quantitative metallographic study was performed on carefully polished metallographic cross sections, monitoring sampling fields of 4500 × 1000 µm² using the back scatter contrast of an analytical scanning electron microscope; evolutions of pore sizes and pore form factors were analyzed and all important details which were previously revealed in a synchrotron study could be reproduced. In addition, it was observed that micro cracks form at larger cast pores. They interlink and thus initiate final rupture. The [110] tensile creep tests showed lower rupture strains than the [001] experiments. In agreement with earlier work, this can be rationalized on the basis of aligned porosity along primary dendrites.     

聚酯纤维机织物-聚氯乙烯-聚偏氟乙烯膜材双轴剪切力学性能试验

为研究聚酯纤维机织物-聚氯乙烯-聚偏氟乙烯(P-PVC-PVDF)膜材的双轴剪切力学性能,提出了工程剪应变计算方法、改进的剪应力计算方法和应力加载方法。基于自主研制的双轴拉伸试验机,对P-PVC-PVDF膜材进行了双轴剪切力学性能试验,得到了膜材剪应力-剪应变曲线、剪切模量和滞回环面积。分析结果表明,剪应力由正变为负后,各力学参数有所差异,但均在加载一次后趋于稳定。当剪应力的上下限设定为±2kN/m时,稳定后的剪切模量范围为11~13kN/m。通过对比证明,主轴与加载方向的夹角变化对计算结果影响不大。研究成果对膜结构设计与分析具有参考价值。     

东莞环球财富大厦地下室混凝土结构温差效应分析

结构超长、复杂体型的地下室混凝土结构,具有较为显著的温度响应,在结构分析、设计与施工阶段需合理考虑环境温差效应。在综合考虑施工进度、后浇带设置、含地下室桩筏基础有限约束刚度、依时温差作用取值的基础上,结合混凝土收缩徐变时效特性等关键因素,建立了一套适用于地下室混凝土结构温差效应分析的精细化仿真分析方法。基于所述方法,开展了东莞环球财富大厦地下室混凝土结构施工及使用全寿命内温差效应的定量分析,明确了结构温差作用下受力较不利构件及变形较大部位,针对性提出结构优化设计建议及施工控制措施,相关成果可为地下室混凝土结构设计提供参考。     

双轴受压下再生混凝土氯离子扩散规律

为了研究复杂应力状态下再生混凝土的氯离子传输特性,首先通过破碎不同水灰比的母体混凝土得到不同性能的再生粗骨料,并对天然混凝土和不同性能再生混凝土进行双轴受压试验。然后利用电场加速氯离子扩散和双轴受压装置测试了不同类型再生骨料混凝土和天然骨料混凝土在不同应力水平和不同应力比下的氯离子扩散系数,并利用压汞仪测试了混凝土内部的微观孔隙结构。最后建立了考虑双轴应力水平、再生骨料吸水率和粗骨料体积分数的再生混凝土氯离子扩散系数理论模型,并进行了试验验证。结果表明:来自不同母体混凝土的再生骨料中的附着老砂浆具有不同的孔隙结构,再生混凝土中老砂浆的孔隙率随着母体混凝土水灰比的增加而变大,进而影响再生混凝土的氯离子扩散性; 应力比相同时,随着双轴受压应力水平的增加,再生混凝土氯离子扩散系数普遍呈现先下降再上升的趋势,在应力水平约为0.5时再生混凝土氯离子扩散系数出现最小值; 在双轴受压荷载作用下,母体混凝土水灰比分别为0.4,0.5,0.6的再生混凝土氯离子扩散系数最多分别下降到无荷载时的0.76%,0.78%,0.78%。     

PVP修饰石墨烯对SBS改性沥青流变性能的影响

为研究经聚乙烯吡咯烷酮(PVP)处理后的石墨烯对SBS改性沥青流变性能的影响,通过高速剪切机在SBS改性沥青中掺入PVP修饰石墨烯,制备了石墨烯-SBS复合改性沥青,并采用动态剪切流变仪、温度扫描和线性振幅扫描试验,对复合改性沥青流变性能及抗疲劳性能变化规律进行研究,同时结合弯曲梁流变仪试验探索了复合改性沥青低温抗裂性的变化规律.试验结果表明:PVP修饰石墨烯的掺入能够有效改善SBS改性沥青在高温条件下的抗变形、弹性恢复能力以及抗疲劳性能;PVP修饰石墨烯的掺入对复合改性沥青的低温抗裂性能存在负面影响,但影响不明显.     

Pseudoelasticity of Metal Nanoparticles Is Caused by Their Ultrahigh Strength

An assembly of hemispherical Ag nanoparticles is prepared by solid‐state dewetting of thin Ag film deposited on the sapphire substrate. The in situ nanomechanical compression testing of the particles with a flat diamond punch inside the scanning electron microscope demonstrates the deformation behavior typical for the nucleation‐controlled plasticity: high elastic deformation followed by an abrupt particles collapse. The latter is associated with the dislocations nucleation in otherwise pristine particle. The average contact pressure in the contact zone at the onset of dislocation‐controlled plasticity is about 8 GPa, and does not depend on particle size. This observation supports the hypothesis that the pseudoelasticity of much smaller Ag nanoparticles is intrinsically related to their ultrahigh strength. A stress‐induced diffusion along the particle–substrate and particle–punch interfaces is identified as a factor controlling the pseudoelastic deformation. The corresponding diffusion model allows estimating the room‐temperature self‐diffusion coefficient of Ag along the Ag–W and Ag–zirconia interfaces, which is quite close to the estimated value of the grain boundary self‐diffusion coefficient in Ag. Based on this finding, the map of pseudoelastic deformation of crystalline materials is proposed.